1. Technical Field
The present invention relates to a cooling system for automotive vehicles, and more particularly relates to an improved cooling system in which liquid coolant is subjected to a comparatively low system pressure, resulting in a reduced boiling point for the liquid coolant, thus enabling the engine being cooled to operate at a controlled temperature under the influence of a thermostat in the cooling system.
2. The Prior Art
Liquid cooling systems for present-day automotive vehicles are pressurized to approximately 15 psi by use of a spring-loaded pressure radiator cap. When the liquid coolant is a 50--50 mixture of water and commercial anti-freeze coolant, the boiling point of the coolant is elevated to approximately 262.degree. F. The prevailing theory is that this pressurization and elevated boiling point is necessary to allow the radiator to retain as much coolant as possible to cool the engine.
In fact, this prevailing cooling method for today's automobiles is contrary to conventional practice, as a result of which the problems of engine overheating, and the deterioration of engine cooling systems have been magnified rather than decreased or eliminated. In high pressure liquid cooling systems which operate at high temperatures, the entire system including the radiator and water pump can be destroyed rather rapidly.
In view of the above, the primary object of the present invention is to provide an engine cooling system which allows the engine to be operated in a strictly controlled temperature range under influence of a thermostat, typically a 195.degree. F. thermostat. The controlled cooling system according to the present invention forces the engine to operate at its thermostat temperature, without substantially overheating or underheating.
When the liquid coolant of a cooling system becomes heated, it must expand, causing an increase in pressure. The present invention allows the coolant to expand without a significant increase in system pressure as normally caused by the pressure cap on the radiator, which cap the invention does not employ. Consequently, with cooling system pressure markedly reduced, the boiling point of the coolant is correspondingly reduced and this allows the system to conform to a well-known principle of physics, i.e. the lower the pressure the lower the boiling point of a liquid. For a liquid to perform as a good coolant, it must have a low boiling point. This phenomenon is made use of in mechanical refrigeration systems where the boiling point of the most commonly used refrigerant R-12 boils at -21.7.degree. F. Once a liquid reaches its boiling point, it can become no hotter as a liquid. The temperature of a liquid coolant at the boiling point is a major concern. The lower the boiling point temperature of the coolant, the greater the amount of heat which it can extract by conduction from the engine. High pressure, high boiling point liquids can naturally extract less heat from an engine, and it is this situation in the prior art which the present invention seeks to eliminate.
The Environmental Protection Agency requires that new automobiles be equipped with 195.degree. F. thermostats. The Agency knows that this is the proper operating temperature to achieve best engine performance and best fuel efficiency with the least pollution. The difficulty is that the 195.degree. F. thermostat in the modern automobile remains closed only until the cold engine, after starting, reaches the optimum thermostat temperature. At all other times, the 195.degree. F. thermostat will remain open because the pressurized cooling system has been designed to operate in the range of 220.degree. F. to 240.degree. F. Thus, with the modern-day engine cooling system, the thermostat does not and cannot control the operating temperature of the engine as it was intended to do. The operating temperature of the engine is actually 25.degree. F. to 45.degree. F. above the temperature which the thermostat was designed to maintain. This elevated engine operating temperature results in excessive fuel consumption, greater atmospheric pollution and more rapid deterioration of the cooling system.
Similarly, most automotive pollution control systems have a thermostat controlled bypass. Since most engines operate at temperatures far above this thermostat setting, to save overheating, the pollution control system is bypassed, rendering the system ineffective most of the time.
Clutch fans are provided in automobiles to blow air over the engine to assist in cooling. These fans are thermostatically controlled as an economy measure to lessen strain on the engine. The fans engage at approximately 225.degree. F. When the automotive engine is equipped with a cooling system thermostat, such as a 195.degree. F. thermostat, and this thermostat is allowed to actually control engine temperature, as indeed occurs with the present invention, the cooling fan would never require activation. However, with the prevailing high pressure-high temperature cooling systems, the cooling fans operate most of the time.
Under actual testing of the present invention, during afternoon temperatures slightly in excess of 100.degree. F., with a 195.degree. F. thermostat in the system, the engine operated at this temperature. With a 180.degree. F. thermostat, it operated at 180.degree. F. With the thermostat removed entirely, allowing free flow of the coolant, the engine operated at 145.degree. F. Thus, according to the present invention, the operating temperature of the engine is truly controlled as it should be by means of the cooling system thermostat. With the low pressure, low temperature cooling system of the present invention it is virtually impossible to overheat the system, and this feature is in accordance with another main objective of the invention.
Other features and advantages of the invention will become apparent to those skilled in the art during the course of the following detailed description.